Loudspeaker, sound reproducing instrument, and the like



R. R. GLEN 2,071,828 LOUDSPEAKER, SOUND REPRODUCING INSTRUMENT, AND THE LIKE Feb. 23, 1937.

Filed 00b. 16, 1934 Patented Feb. 23, 1937 UNITED STATES PATENT OFFICE INSTRUMENT,

Robert Rodger Glen's Patents and AND THE LIKE Glen, Anglet, France, assignor to Holdings, Inc., New York,

N. Y., a corporation of Delaware Application October 16, 1934, Serial No. 748,474 In Great Britain June 19, 1934 Claims.

This invention relates to improvements in loud speakers, sound reproducing instruments, and the like, which are of the kind having a ,diaphragrn that is vibrated by an electrical driving unit. The object of the invention is generally to improve the tone quality of such instruments.

In accordance with the present invention, a loud speaker or the like is provided with a pair m of diaphragms, one of which is driven by a driving unit, while the second diaphragm is spaced away from the first diaphragm and unconnected thereto, but is driven from the first solely by the vibration and/or compression of the air in the space between the two diaphragms.

The pair of diaphrag'ms may be either of the same diameter or of different diameters, the

specific design adopted depending on the acoustic effect that it is desired to produce.

2 Other objects of the invention will in part be obvious and will in part appear hereinafter. For a fuller understanding of the nature and objects of the invention reference should be had to the following detailed description taken in connection with the accompanying drawing, in which:

Fig. 1 is a sectional elevation of a loud speaker according to the invention with the casing and auxiliary parts removed; and 30 Fig. 2 is an enlarged sectional elevation of the apices of the cones.

Referring now to the drawing, and particularly to Fig. 1, the loud speaker shown has a permanent magnet ll) of known form with .an

35 annular moving coil ll connected by a bridge l2 to a driving. cone l3 by a rod I4. The cone I3 is secured at its periphery on a suitable ring l5 for example, one of aluminum, that has depending arms IG which are spaced around the 40 ring and connected at their other ends to a ring I! that is ailixed to the permanent magnet H).

A driven cone l8, shown as considerably larger than the driving cone I3, is secured to a suitable supporting ring IQ, for example, one of 45 aluminum, that is carried on a spider 20, which in turn engages the permanent magnet Ill through a base ring 2|.

An advantageous arrangement of the cones is shown in the drawing, particularly in Fig. 2,

o where it is seen that the cones are coaxial, the smaller end of the larger cone l8 being parallel with the smaller cone l3; the cones also being uniformly spaced apart a short distance so that there is no connection between them except through the spider 20 and the arms IS. The

cones may be of any suitable material, for example, the smaller cone may be of spun aluminum, while the larger cone may be of papier mache impregnated or dressed with a suitable stiffening or loading substance, such as a mixture comprising fish glue, bitumen, pumice, gypsum, or the like.

The actuating force is transmitted from the driving cone I3 to the driven cone I8 solely by way of acoustic vibrations in the intervening air gap. To this end, the air gap is proportioned to produce this effect to substantially a maximum extent, as it is found that by this arrangement the penetration of the sound emitted is greatly increased and intensified, efiective reproduction over a relatively wide range of frequencies being thereby obtained, while at the same time the volume of sound produced is not diminished as compared with loud speakers of known construction.

In the form here shown, the cone I8 is considerably larger than the cone Hi, In one embodiment, that has been found successful, the diameter of the cone I8 is about 14% inches and the diameter of the cone I3 is from 4 to 6 inches. The distance between the two cones, measured normal to their surfaces, is 3/64ths of an inch.

In the practice of the invention, cones of relatively small angles may be used. Also, it will be understood that, while a coaxial arrangement of the cones has certain advantages, this is not a necessary arrangement, nor is the spacing of the cones necessarily uniform or confined to one employing parallel cones; a degree of divergence from the parallel arrangement may be employed so long as the second cone is driven by the first through air vibrations. The driving unit of the loud speaker, of course, forms no part of the present invention; any suitable unit may be employed to this end.

The invention may be applied to any purpose to which loud speakers are usually put, such as radio reception and reproduction of gramophone records, but has particular application to acoustical apparatus for public address systems, for places of public concourse, entertainment, and the like.

Since certain changes may be made in the above construction and different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In loud speakers and the like, the combina tion with a driving unit, of a driving diaphragm connected to be actuated by said unit, and a second diaphragm independently mounted in substantially parallel spaced relation to the first said diaphragm; the intervening space being in free communication with the atmosphere and of a width such that said second diaphragm is driven from the first solely by the acoustic vibration of the air in the space between said diaphragms.

2. In loud speakers and the like, the combination with a driving unit, of a conical diaphragm mounted adjacent said unit and connected to be actuated by said unit, and a second conical diaphragm of larger diameter than the first independently mounted and disposed substantially coaxially therewith in parallel spaced relation to the first said diaphragm; the intervening space having unobstructed communication with the surrounding atmosphere and of a width such that said second diaphragm is driven from the first solely by the acoustic vibration of the air in the space between said diaphragms.

3. In loud speakers and the like, the combination with a driving unit, of a conical diaphragm mounted adjacent said unit and connected to be actuated by said unit, and a second conical diaphragm similar to the first said diaphragm and of larger diameter mounted coaxially with the first diaphragm, unattached thereto, and uniformly spaced therefrom; the intervening space having unobstructed communication with the surrounding atmosphere and of a width such as to transmit driving force from the first diaphragm to the second through acoustic vibration of the air in said space substantially to a maximum extent.

4. In loud speakers and the like, the combination with a driving unit, of a pair of unbacked spaced parallel supporting rings attached to said driving unit, a relatively small cone mounted on the closest supporting ring and connected to be actuated by said unit, and a second similar cone mounted on the other ring substantially parallel to and coaxial with the first said diaphragm and mechanically unattached thereto, said rings being positioned to provide an intervening space between said diaphragms having a ratio of thickness to diameter not greater than one to one hundred and such that driving force is transmitted from the first said diaphragm to the second through the acoustic vibration of the air in said space.

5. In loud speakers and the like of the character set forth in claim 4, an arrangement of cones in which the spacing is uniform and of the order of 3/64th of an inch.

ROBERT R. GLEN. 

